THE INFLUENCE OF EMITTER-BASE JUNCTION DESIGN ON COLLECTOR SATURATIONCURRENT, IDEALITY FACTOR, EARLY VOLTAGE, AND DEVICE SWITCHING SPEED OF SI SIGE HBTS/

In advanced Si/SiGe HBT's the base is doped much higher than emitter a nd collector. Base outdiffusion becomes a problem because of the forma tion of parasitic barriers that degrade device performance. The simula tions and experiments of this paper show that a strong correlation exi sts between (a) the drop of the collector saturation current, (b) an i ncrease of its ideality factor and (c) a rise of the switching time du e to an additional emitter delay which can no longer be neglected. Cur ves of these three parameters as a function of Si/SiGe heterointerface position and outdiffusion at the base-emitter interface have been cal culated and indicate that only a few nm shift may cause severe device degradation. An important result is that the collector current idealit y factor or the inverse Early voltage is a very sensitive indicator fo r the quality of the emitter-base interface. Application of these resu lts have yielded experimental SiGe HBT's with transit frequencies abov e 60 GHz.